First I apologize to Mme. Curie for missing her point about nuclear and nucleus. In my mad dash to jump on my horse and ride off in all directions I didn't notice that she was pointing out that you don't hear people saying nuculus for nucleus. There are at least two reasons for this. One of the reasons for the pronunciation nucular is that there is an extensive support system of other words ending in -cular, approximately four times as many as words ending in -culus given the relative numbers m-w.com gives when fed "*cular" versus "*culus". The other reason is that nuclear is considerably more common than nucleus with 7,410,000 google hits for nuclear versus 967,000 for nucleus. I suspect that if you listen you will hear nuculus, just not nearly as often as nucular.
The point of the thumb thing was that it is a set pattern in your muscles as is pronunciation.
As for intelligence having an effect on our ability to alter speech patterns learned early in life I have merely to point out that many otherwise intelligent people have great difficulty learning new languages after childhood and often those that do never speak it with a good accent. On the other hand, many people of average intelligence or below learn to speak foreign languages late in life and can speak like a native.
As for learning new pronunciations, the President of the United States has plenty more important things to worry about than how to pronounce nuclear. He could be coached for hours and practice saying "NOO-CLEE-ER" for hours and then have it all dissipate when he's up at the speaker's platform, as anyone who has experienced public speaking knows well.
